Calculate compression ratio from compression tester result

[JonB]

Hi

Bit of a technical one, this.. Can the Twink's compression ratio be worked out (even approximately) from the readings taken from a compression tester?

For example, I measured 192, 196, 199, 210 PSI respectively in a cold crank test (albeit with the throttle closed) for cylinders 1,2,3,4 respectively. Is there a formula for calculating the compression ratio from these?

Ta muchly
JonB

[promotor]

I'd say it would be hard to get an accurate compression ratio figure - different cams will give different readings, cam timing and even small things like how loose or tight cam/valve clearance figures are will make a difference. Piston ring sealing will also vary results so it would be an educated guess.

[john.p.clegg]

Have a look at ..

https://web.archive.org/web/20110903073 ... 0/comp.htm

John

[JonB]

Thanks John, very useful. I'm figuring something like 10.5:1 ratio but I will do another test once the engine is running.. in about 100 years at this rate...

[Donels]

That's a cracking document. Very interesting.

[Spyder fan]

If I remember correctly the standard compression ratio for a lotus twin cam of your cars vintage is 9.5:1

No doubt those with more definite knowledge will be along shortly. 10.5:1 would be a modified/uprated engine

[JonB]

Interesting, Alan. It's an S/E engine with a D cam. I've seen these engines referred to as "Super S/E".